Friday, 19 October 2007

Pacific Insects is Online

In what is sure to bring rejoicing to all entomologists and other people who work with insects in the South Pacific, the good people at the Bishop Museum have put the back issues of Pacific Insects online. Unfortunately, the journal isn't being published anymore, but it's great to have this valuable resource right at our fingertips...


Homona mermerodes eats a lot.

With the advent of cheap and effective DNA amplification and sequencing methods, there has been an increased appreciation of biological diversity. In particular, a field that has particularly benefited from the techniques has been the detection of cryptic species. These are groups of organisms that appear the same, but a look into the DNA of the creatures reveal that they are complexes of genetically different populations. Frequently, these cryptic species are found to be host specific to certain food types, while the former "superspecies" was thought to have a range of hosts.

There has been a lot of work done recently on the northern coast of Papua New Guinea by the Binatang Research Centre. Their research has a focus on rainforest invertebrate dynamics and ecology, and they have done a sterling job in encouraging science in the country. They've trained several PNG citizens as parataxonomists, and a look at their publication list is rather impressive. As part of this research, they have investigated the population structure of the leafroller moth Homona mermerodes (Lepidoptera: Tortricidae). They used the fabled cytochrome oxidase gene (commonly abbreviated to cox1 or COI) to investigate whether the species is a widespread polyphagous species, or whether it is made up of a lot of cryptic species that are specific to certain plants. The COI gene is found in the mitochondrial DNA, and is famous as the gene of choice for what has become known as barcoding. This is an ambitious scheme to sequence the COI gene region for every organism on the planet to allow it to be quickly and easily identified.

Hulcr et al published the results of the work on Homona in Molecular Ecology Notes in July this year. Their analysis shows that the use of COI made some very nice distinct groups (clades), with big differences between the different clades. The interspecific genetic distances are larger than the intraspecific distances, forming a bimodal (twin-peaked) distribution with very marginal overlap. There were certainly no genetic differences between H. mermerodes reared on different plants, nor were there major differences between PNG and Australian (Queensland) populations.

One of the things that impressed me by this paper was the incorporation of pictures of the moth including both adult, larvae, and genitalia. It has been a concern of mine that much of the rhetoric surrounding barcoding seems to neglect other taxonomic evidence, whether it's morphological or other genes. I believe this is from the enthusiasm surrounding the power of the techniques as opposed to deliberately believing that barcoding is the ONLY way. Single-character taxonomy will always provide misleading results, whether it's in a morphological sense, or if it's only single gene region being looked at. I have experienced this myself when trying to identify things and getting involved with single things rather than looking at the organism as a whole. Good taxonomy takes a lot of information into account in order to try and infer species limits.

It is also good to have an example where a wide ranging, generalist and morphologically variable species has a well-defined genetic structure. Frequently it seems that the genetics of creatures that display these traits suggests that there are a number of cryptic species. It is gratifying (to me at least) to know that these cryptic species groups aren't a given. Further research that attempts to deduce the factors that influence the formation of cryptic species groups will be highly interesting.

Hulcr J, Miller SE, Setliff GP, Darrow KA, Mueller ND, Hebert PDN, Weiblen GD. 2007
DNA Barcoding confirms polyphagy in a generalist moth, Homona mermerodes (Lepidoptera: Tortricidae).
Molecular Ecology Notes 7: 549-557

Belligerent newcomers and shrinking wings - Carabid Ecology on Maui

To make use of an allusion from literature, things are rotten in the Hawaiian Islands. Like many places, they are being overrun by Argentine ant (Linepithema humile) (Hymenoptera: Formicidae). Coupled with this, they also have a carabid beetle, Trechus obtusus that is running amok over the island of Maui. Stuck in the middle are a number of endemic carabids in the genus Mecyclothorax.

James Liebherr and Paul Krushelnycky have published a paper detailing the plight of the Mecyclothorax over the past seven years, and it makes for interesting reading. In a nutshell: Trechus obtusus was first found on the island of Maui in 1999 (sounds familiar…) and increased dramatically, such that a 4m2 collection of leaf litter in 2001 had 77 beetles in it. The numbers of Mecyclothorax since that time have had a statistically significant decline since then, while T. obtusus numbers remain approximately the same. The presence of ants is also an important predictor in whether or not Mecyclothorax is present in an area or not. The numbers of Mecyclothorax are significantly lower in ant-infested areas, while the abundance T. obtusus is not significantly affected by Argentine ants. It looks grim for Mecyclothorax, but the authors do not seem to express any pessimism about the future of the beetles.

Another interesting aspect about the system is how Trechus obtusus is losing its wings. T. obtusus has two forms - a fully winged (macropterous) form that can fly around, and a short winged (brachypterous) form whose wings reach halfway down the abdomen and is flightless. There has been a very rapid change in the proportion of wing forms in populations of T. obtusus on Maui. In one site, 0% of beetles collected in 2001 had short wings. Four years later, in 2005 15% of beetles collected were brachypterous. At another site the proportions have increased from 0% brachyptery to 18% in three years. This change has a number of possible consequences. It is hoped that the decrease in numbers of flighted individuals will help prevent T. obtusus from spreading to other Hawaiian Islands. However, this does not prevent it from invading through human transportation, which is the most likely way it got to Maui in the first place. Second, the dimorphism of T. obtusus will no doubt help it spread around Maui to a much greater extent, and form more stable populations, than the endemic Mecyclothorax which are exclusively brachypterous.

Wing dimorphism is considered to be determined by a single allele. Individuals with full wings are thought to be homozygous recessive, while shorter wings can be heterozygous or homozygous dominant. While the authors suggest that all of the first beetles to arrive were macropterous (i.e. homozygous recessive), this would seem to indicate that there would be no alleles for brachyptery in the population. The situation here probably suggests that wing size in carabids is slightly more complicated than classical Mendelian genetics, and that more than one allele influences the size of wings in Trechus obtusus.

The influence of Argentine ant on the populations of carabid beetles is also pretty scary. Argentine ant is one of the world's worst invasive ant species and it is established in Hawaii, New Zealand and Australia. It is not found elsewhere in the Pacific. It is one of the species on the Pacific Ant Prevention Plan and it is hoped that it doesn't get established. The carabids elsewhere in the Pacific are not well known, and their response to Argentine ant invasion would probably be similar to the situation in Hawaii.

The globalisation of biodiversity has had a huge impact on native ecosystems. It looks set to continue, despite advances in biosecurity policy and techniques. It looks gloomy, and to an extent it is. However, nature has survived this long, and will continue to get by, though in a slightly more impoverished state. Another aspect of invasions that I haven't looked up yet is the beneficial side, where new organisms enrich and add to the indigenous ecosystem. Does it happen? I don't know, and it's not something you hear about. Maybe an idea for someone?

Liebherr, JK; Krushelnycky PD. 2007.
Unfortunate encounters? Novel interactions of native Mecyclothorax, alien Trechus obtusus (Coleoptera: Carabidae), and Argentine ant (Linepithema humile, Hymenoptera: Formicidae) acress a Hawaiian landscape.
Journal of Insect Conservation 11:61-73

Thursday, 18 October 2007

Fiji Arthropods No. 9 OUT NOW!!!

The latest installment of the results from the NSF funded Fiji Arthropod Survey is online now at the their webpage. Check it out to get the goss on Fijian Sciarids, Scelionids, Orthopterans and Mealybugs...

French Polynesia and the invasion of the Cicadellids...

1999 was a bad year for French Polynesian plants. In that year two species of highly generalist leafhoppers (Homoptera: Cidadellidae) were found on Tahiti. These were the catchy-named but highly harmful glassy-winged sharpshooter (Homalodisca vitripennis) and the two-spotted leafhopper (Sophonia orientalis). Since then the two have spread around French Polynesia, and are now in the Austral Islands and the Marquesas. In doing so, they have sparked a frenzy of research into their biology which has revealed a number of taxonomic difficulties. The story provides insight into the importance of good taxonomy, and its usefulness in real life.

The glassy-winged sharpshooter aptly got a lot of attention from its bold invasion. The insect is a hugely important vector for a number of plant diseases, is large, and is easily transported. It also excretes a lot of watery fluid, weakening plants and causing a nuisance for humans. As an added twist, it poisons predators that try to eat it. Since then it has been the subject of a biocontrol programme with the wasp Gonatocerus ashmeadi (Hymenoptera: Mymaridae).

While this was happening, the two-spotted leafhopper was slipping under the radar. My attention was brought to it when reading a paper by Aguin-Pombo, Aguiar and Kuznetsova in the Annals of the Entomological Society of America. The insect has made a hop over to the eastern Atlantic island of Madeira, where it was discovered in 2000. In their paper, Aguin-Pombo et al summarise what is known about the leafhopper, which has made itself a nuisance in Hawaii, California and now Madeira. They also provide a redescription of the insect, and comment on its taxonomy.

It turns out that there is a lot of confusion in the literature regarding the correct name and identity of the leafhopper. In this paper, the authors follow the rather convoluted path to the leafhopper's currently accepted name of Sophonia orientalis. Unfortunately though, there remains some confusion, in that the name given in most of the biological literature is S. rufofascia, currently a synonym of S. orientalis. The confusion seems to have arisen through a combined effect of scattered taxonomic literature, poor and incomplete descriptions, differing taxonomic opinion, and the inability to access type specimens. This is unfortunate, particularly in the situation of biological invasions, where it is necessary to quickly and confidently identify the species in question in order to evaluate the possible impact and to put managment strategies in place.

The taxonomic confusion hasn't been all one way though. I see that the glassy-winged sharpshooter has also had a recent name change from Homalodisca coagulata to H. vitripennis. The paper by Takiya, McKamey and Cavichiolil informing of the change is a paper of fine taxonomic detective work, and a good explanation of the rationale behind the change.

The Aguin-Pombo et al paper is also a good example of how taxonomic literature can be incorporated with other information to produce a much more useful document than a description of a single species. This has been the subject of discussion amongst some of my colleagues recently, and it is good to have a recent example. As well as the description, the paper by Aguin-Pombo et al incorporates karyological results (chromosome stuff) and information on the host plants, abundance, and establishment of the two-spotted leafhopper on Madeira.

It is unfortunate that these species invasions occurred at the same time, as resources which could have been used to control the two-spotted leafhopper were used to combat the sharpshooter. While the sharpshooter is an important pest, the leafhopper is not negligible either. In Hawaii and Madeira, it has been found to be malevolent towards banana, taro, sweet potato, papaya and mango - all of which are important food plants in the South Pacific.

The whole scenario is a good case study of the practical importance of taxonomy, and the necessity of good taxonomic work in the first place. It's a timely lesson for those of us entering the field, which we'd do well to heed.

Aguin-Pombo A, Aguiar AMF, Kuznetsova VG. 2007
Bionomics and taxonomy of leafhopper
Sophonia orientalis (Homoptera:Cicadellidae), a Pacific pest species in the Macaronesian archipelagos.
Annals of the Entomological Society of America 100(1): 19-26